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How to convert IGN X,Y,Z coords to GPS

OK having a brain fart ;-( Lots of the Series Blue Mpas have coords for cave sites, but they're not GPS coords. Ideally I'd like to find a formula for doing the conversions - I'm a java programmer so would like to knock up a spreadsheet / java program to do the conversions, but don't really understand the lingo / issues involved. Anyone know how to do the conversions/ is there some site that explains it in plain english???
Thanks in anticipation

Re: How to convert IGN X,Y,Z coords to GPS

Originally Posted by gallathan

OK having a brain fart ;-( Lots of the Series Blue Mpas have coords for cave sites, but they're not GPS coords. Ideally I'd like to find a formula for doing the conversions - I'm a java programmer so would like to knock up a spreadsheet / java program to do the conversions, but don't really understand the lingo / issues involved. Anyone know how to do the conversions/ is there some site that explains it in plain english???
Thanks in anticipation

Re: How to convert IGN X,Y,Z coords to GPS

First a health warning: I have never had to deal with French maps so I might be missing something but the following should work.

The setup menu in a GPS usually gives you the option to change the grid system it operates in - Lat/Long, British National Grid, UTM etc. If yours has the option to use NTF (New Transform France) then that's all you need to do. Otherwise set it WGS84 and UTM and then use the simple conversion in the coordinates .pdf to correct the position the GPS gives you.
Or you could wait until IGN issues the map with a UTM grid but that might take a while.

Re: How to convert IGN X,Y,Z coords to GPS

There is a piece of software on the IGN website which will do the translation. The minor problem is that you have to know which regional version of the co-ord system your location is in or if it is using the generic system...

The simplest thing, find the cave with a map (and compass if necessary) on foot, stand by the entrance, press the waypoint button on your GPS. It saves the permanent loss of higher brain function and thoughts of suicide which trying to figure out the Lambert sysem causes :D